Temporal range: Early Cambrian[1][2] – Late Permian,
Trilobita Diversity.png
Montage of trilobite genera: Top row: Walliserops, Phacops and Cambropallas; bottom row: Isotelus, Kolihapeltis and Ceratarges
Scientific classification e
Kingdom: Animalia
Phylum: Arthropoda
(unranked): Artiopoda
Subphylum: Trilobitomorpha
Class: Trilobita
Walch, 1771[3]

Trilobites (/ˈtrləˌbts, ˈtrɪlə-/;[4][5][6] meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the Atdabanian stage of the Early Cambrian period (521 million years ago) and they flourished throughout the lower Paleozoic before slipping into a long decline, when, during the Devonian, all trilobite orders except the Proetida died out. The last extant trilobites finally disappeared in the mass extinction at the end of the Permian about 252 million years ago. Trilobites were among the most successful of all early animals, existing in oceans for almost 270 million years, with over 22,000 species having been described.

By the time trilobites first appeared in the fossil record, they were already highly diversified and geographically dispersed. Because trilobites had wide diversity and an easily fossilized exoskeleton, they left an extensive fossil record. The study of their fossils has facilitated important contributions to biostratigraphy, paleontology, evolutionary biology, and plate tectonics. Trilobites are often placed within the arthropod subphylum Schizoramia within the superclass Arachnomorpha (equivalent to the Arachnata),[7] although several alternative taxonomies are found in the literature. More recently they have been placed within the Artiopoda, which includes many organisms that are morphologically similar to trilobites, but are largely unmineralised.

Trilobites evolved into many ecological niches; some moved over the seabed as predators, scavengers, or filter feeders, and some swam, feeding on plankton. Some even crawled onto land.[8] Most lifestyles expected of modern marine arthropods are seen in trilobites, with the possible exception of parasitism (where scientific debate continues).[9] Some trilobites (particularly the family Olenidae) are even thought to have evolved a symbiotic relationship with sulfur-eating bacteria from which they derived food.[10] The largest trilobites were more than 45 centimetres (18 in) long and may have weighed as much as 4.5 kilograms (9.9 lb).[11]

  1. ^ Cite error: The named reference lieberman02 was invoked but never defined (see the help page).
  2. ^ Fortey, Richard (2000), Trilobite!: Eyewitness to Evolution, London: HarperCollins, ISBN 978-0-00-257012-1
  3. ^ Robert Kihm; James St. John (2007). "Walch's trilobite research – A translation of his 1771 trilobite chapter" (PDF). In Donald G. Mikulic; Ed Landing; Joanne Kluessendorf (eds.). Fabulous fossils – 300 years of worldwide research on trilobites. New York State Museum Bulletin. Vol. 507. University of the State of New York. pp. 115–140. Archived from the original (PDF) on 2014-07-14.
  4. ^ Jones, Daniel (2003) [1917]. "trilobite". In Peter Roach; James Hartmann; Jane Setter (eds.). English Pronouncing Dictionary. Cambridge: Cambridge University Press. ISBN 978-3-12-539683-8.
  5. ^ "trilobite". Merriam-Webster Dictionary.
  6. ^ "trilobite". Unabridged (Online). n.d.
  7. ^ Cotton, T. J.; Braddy, S. J. (2004). "The phylogeny of arachnomorph arthropods and the origins of the Chelicerata". Transactions of the Royal Society of Edinburgh: Earth Sciences. 94 (3): 169–193. doi:10.1017/S0263593303000105.
  8. ^ "Trilobites ventured beyond the ocean". Nature. 505 (7483): 264–265. January 2014. doi:10.1038/505264e.
  9. ^ Fortey, Richard (2004). "The Lifestyles of the Trilobites" (PDF). American Scientist. 92 (5): 446–453. doi:10.1511/2004.49.944. Archived from the original (PDF) on 2006-09-18.
  10. ^ Fortey, Richard (June 2000), "Olenid trilobites: The oldest known chemoautotrophic symbionts?", Proceedings of the National Academy of Sciences, 97 (12): 6574–6578, Bibcode:2000PNAS...97.6574F, doi:10.1073/pnas.97.12.6574, PMC 18664, PMID 10841557
  11. ^ "Trilobite | fossil arthropod".

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